The purposes of the investigation are (1) to measure the blood flow to the rabbit pancreas: (2) to determine the partition of that flow between the endocrine and exocrine portions of the organ (islets of Langerhans vs. acini); and (3) to study the question of the presence of an insular-acinar portal system. Blood flow to the islets will be measured by combining the use of non-radioactive microspheres which can be located microscopically in the tissues and visualization of the islets by an in situ histological staining procedure.